This invention relates generally to an apparatus for use in the manufacture of trusses and, more particularly, to methods and apparatus for assembling a prefabricated truss.
Prefabricated trusses are often used in the construction of building structures because of their strength, reliability, low cost, and ease of use. The trusses are typically assembled in a factory using machinery for mass-fabrication of individual truss components. The trusses are assembled, for example, on large assembly tables and then shipped to construction sites.
A prefabricated truss typically includes truss members coupled by nailing plates. Each truss member has a first surface and a second surface, and the truss members are pre-cut for a predefined truss configuration. In assembling the truss, the truss members are arranged on a long truss assembly table and nailing plates are placed over the first surface of the truss members. The plates are then pressed into the truss members using, for example, a roller or a vertical press. The truss is then manually flipped over and nailing plates are positioned over the second face of the truss members and pressed thereto. The completed truss is then removed from the assembly table.
Modern gantry presses, or roller presses, include a gantry frame that travels on two guide tracks mounted to the floor along each side of the truss table. A roller is mounted to the gantry frame at a predetermined distance above a truss table worksurface so that as the gantry frame is moved along the guide tracks, the roller presses the nailing plates into the truss members. The gantry press typically presses the nailing plates into the wood truss members to a depth of 50-80% of the total length of the nailing plate projections. The truss may then be passed through a finishing press, which includes a pair of nip rollers, to fully press the nailing plates into the truss members.
The installation of the gantry press guide tracks is critical in the proper operation of the gantry press. In a typical installation, the guide tracks are spaced away from the sides of the truss table to provide adequate clearance for the gantry press. Since the gantry press rides on the guide tracks, the tracks must be level and true with respect to the truss table worksurface. Due to the size and weight of the gantry press, the guide tracks must be securely fastened to the floor and made of a suitable material, typically, steel. During use of the truss table, an operator is required to place the truss members and nailing plates on the truss table worksurface, requiring the operators to step over the guide tracks, if possible, or stand farther from the table and extend the truss members and nailing plates an additional distance. Due to the size and spacing of the guide tracks, easy access to the truss table worksurface is impeded and throughput is reduced.
It would be desirable to provide an apparatus which enables fabricating a truss without requiring that guide tracks be placed on the floor next to the truss table. It would also be desirable to provide an apparatus which does not require a finishing roller to fully press in the nailing plates.
These and other objects may be obtained by a truss assembly apparatus which, in one embodiment includes a substantially rectangular shaped truss table having two longitudinal sides, a worksurface, and two ends. Each longitudinal side includes a substantially C-shaped elongate member, or guide, extending the length of the truss table. At least one camber tube and at least one outer rail are provided to clamp the truss members in position over the worksurface.
The apparatus also includes a roller assembly for pressing the nailing plates into the truss members. The roller assembly includes a substantially cylindrical shaped roller and a substantially inverted U-shaped frame. The roller is rotatably coupled to the frame and sized to press the nailing plates in to the truss members as roller assembly moves between the ends of the truss table. The roller assembly further includes a plurality of drive wheels and a plurality of pressure wheels. Each substantially frustro-conical shaped drive wheel is coupled to the frame and sized to rest on a truss table guide to move the roller assembly relative to the truss table. Each pressure wheel is substantially spool shaped and movably coupled to the frame and sized to rest against the truss table when the roller is adjacent to the truss. A motor is coupled to the roller and the drive wheels to drive the roller and the drive wheels at the same speed. The apparatus moves between the ends of the truss table by rotation of the roller and the drive wheels.
To fabricate a truss using the above described truss assembly apparatus, the truss members are positioned on the truss table worksurface. A first camber tube is then moved toward a first outer rail to clamp, or trap, the truss members in place. The nailing plates are then positioned over the truss member first surfaces and are pressed into the truss members using the roller assembly. Specifically, the roller assembly roller presses the nailing plates into the truss members by moving between the ends of the truss table. The roller assembly is moved by energizing the motor so that the roller and drive wheels rotate. The drive wheels move the roller assembly relative to the truss table until the roller is adjacent the truss members. After the roller is adjacent to the truss members, the roller rolls onto the first surface of the truss and the nailing plates. The nailing plates are fully pressed into the truss members as a result of proper roller and pressure wheel spacing. The roller is spaced above the worksurface so that as the roller rolls onto the nailing plates the roller assembly is raised. This raised position removes the drive wheels from the guides and places the weight of the entire roller assembly on the nailing plates. Additionally, as the roller assembly is raised, the pressure wheels are placed against the truss table so that the upward movement of the roller assembly is limited. While the roller assembly is in the raised position, the rotation of the roller against the truss members and the nailing plates moves the roller assembly relative to the table. After traveling the entire length of the truss, the roller assembly will drop slightly as the roller rolls off the truss so that the drive wheels are placed against the guides. The drive wheels then continue movement of the roller assembly until stopped by the operator or the roller assembly reaches the end of the truss table. The first camber tube is then moved away from the truss members so that the members are no longer clamped in place and the truss is flipped over and placed on the worksurface between a second camber tube and a second outer rail. The second camber tube is moved toward the truss so that the truss is clamped between the camber tube and the outer rail and the nailing plates are positioned over the truss members. After reversing the rotational direction of the motor, the roller assembly is moved between the ends of the truss table in the manner described above so that the nailing plates are press into the truss members. The second camber tube is then moved away from the truss members so that the truss is no longer clamped in place. The truss is then removed from the truss assembly.
The above described apparatus facilitates fabricating a truss without requiring floor mounted guide tracks. In addition, such apparatus presses the nailing plates into the truss members without requiring a finishing press, therefore saving time.